You may have a floater. Please see an ophthalmologist if this is new.
According to me,
Eye floaters can be clumpy or stringy, light or black. They are due to sections or specks of undissolved vitreous gel content sailing in the demolished gel-like liquid (vitreous) in the rear of your right eye, which throw black areas on the retina when mild goes into your right eye. That's why you suffering this kind of problem so you should go for an eye care specialist which suggest you or solve your problem.